THE MUSOULO-CUTANEOUS NERVE. 297 



to about the middle of the arm, where it pierces the fascia, and its filaments are 

 thence continued to the interval between the internal condyle of the humerus and 

 the olecranon. 



Varieties. The small internal cutaneous may receive fibres from the eighth cervical 

 (rarely) or the second dorsal nerve. The connection iriHi flic fateroosto-kufaeral nerve 

 presents much variety in different cases : in some, there are two or more intercommunications. ' 

 forming a kind of plexus on the posterior boundary of the axillary space ; in others the 

 intercosto-humeral nerve is of larger size than usual, and takes the place of the nerve of 

 Wrisberg, only receiving in the axilla a small filament from the brachial plexus, and this 

 small communicating filament represents in such cases the nerve of Wrisberg. It sometimes 

 communicates also with the lateral cutaneous branch of the third intercostal nerve. Absence 

 of the nerve of Wrisberg is noted. 



The nerve to the coraco-brachialis is a small branch formed by fibres 

 derived from the seventh cervical nerve. In the infant it is a separate offset from 

 the outer cord of the plexus, but in the adult it is commonly more or less closely 

 united to the trunk of the mnsculo-cutaneous nerve, from which it separates before 

 that nerve enters the muscle (Herring-ham). It is often represented by two 

 filaments. 



Musculo cutaneous nerve. The musculo-cutaneous or external cutaneous 

 nerve, derived from the fifth and sixth cervical nerves, is deeply placed between the 

 muscles as far as the elbow, and below that point is immediately under 'the 

 integument. Arising from the outer cord of the brachial plexus opposite the small 

 pectoral muscle, it perforates the coraco-brachialis, and, passing obliquely across the 

 arm between the biceps and brachialis anticus muscles, reaches the outer side of the 

 biceps a little above the elbow. Here it perforates the fascia, and, passing behind 

 the median-cephalic vein, divides into two branches which supply the integument 

 on the outer side of the forearm, one on the anterior, the other on the posterior 

 aspect. 



A. Branches in the arm. 



In addition to the one or two twigs to the coraco-brachialis which may be given 

 off from this nerve near its origin (see above), the musculo-cutaneous furnishes the 

 following offsets in the deep part of its course : 



(a) Branches to the biceps and brachialis anticus muscles, which arise after the 

 nerve has pierced the coraco-brachialis. 



(b) A slender branch to the humerus, entering the bone with the medullary 

 artery. 



(c) An articular filament to the elbow-joint. 



The nerve to the humerus is described by Rauber and others as arising from the nerve 

 before it enters the coraco-brachialis, and descending along the brachial artery, to which it 

 supplies filaments ; but Testut states that in all the cases in which he found this branch it 

 was given off by the nerve to the brachialis anticus. An articular filament may proceed from 

 the nerve to the biceps (Cruveilhier) or from that to the brachialis anticus (Riidinger) ; 

 Testut traced a twig from the latter source to the periosteum about the coronoid fossa. A 

 vascular branch to the lower part of the brachial artery from the nerve of tho brachialis 

 anticus is described by Swan and Testut. 



B. Branches in the forearm. 



(a) The anterior branch descends near the radial border of the forearm. It is 

 placed in front of the radial artery near the wrist, and distributes its terminal offsets 

 over the thenar eminence. One or two filaments pierce the fascia and run on the 

 artery to the articulations of the wrist. This part of the nerve is connected above 

 the wrist with a branch of the radial nerve. 



(b) The posterior branch is directed outwards to the back of the forearm, and 



